1. Field of the Invention
The present invention relates to a pulse position measurement type meter-driving circuit which measures the distance between the edges of externally-input successive pulses and which controls the display of the meter or the position of the indicating needle thereof in accordance with the distance between the pulse edges. In particular, the meter-driving circuit is advantageously applied to the processing of output data in the case where the distance between the pulse edges varies greatly.
2. Description of the Related Art
A pulse position measurement type meter-driving circuit measures the distance between the edges of externally-input successive pulses and executes processing in accordance with the measurement. The operation of this circuit will be described, with reference to the timing chart shown in FIG. 1. As is understood from the timing chart, a pulse control circuit generates a latch signal EG and a resetting signal ER in response to edges of input pulses IN. A binary counter measure the time corresponding to the distance between the edges of two successive input pulses IN, by counting reference clock pulses supplied thereto. After the count is reset by the resetting signal ER, the binary counter measures the time corresponding to the distance between the edges of the next two successive input pulses IN. The time measured by the binary counter is output as measurement data DAT, each time the count of the binary counter is reset.
When the time interval between two successive latch signals EG is being counted up by the binary counter, measurement data DAT corresponding to the time interval between the preceding two successive latch signals EG is continuously output. In other words, measurement data DAT is determined after one edge (rise) of the input pulse IN is detected and when the next edge thereof has just been detected. For example, data regarding time T1 corresponding to the distance between the edges of two successive input pulses IN is continuously output during time T2 corresponding to the distance between the edges of the next two successive input pulses IN. In accordance with the data, the display of the meter or the position of the indicating needle thereof is determined.
There may be a case where no pulse edge corresponding to the end of the measurement is entered after the detection of a pulse edge corresponding the start of measurement. Also, there may be a case where the time interval between the two successive pulse edges is far longer than the time interval between the preceding two successive pulse edges. In such cases, the output of the measurement data corresponding to the preceding edge-to-edge distance is continued even after the detection of the pulse edge corresponding to the start of the measurement. In other words, the output measurement data does not always reflect the actual measurement.